This Merit proposal is part of a BLR&D Collaborative Merit Award for TBI (CTBI) proposal (RFP #BX-19- 006) involving three separate but integrated proposals that together investigate the mechanisms by which TBI enhances impulsivity and suicidal behavior in Veterans. The rationale for the collaborative project is to combine neurobiological mechanistic studies in animals with human imaging and biomarker analysis to understand the manner in which TBI influences impulsivity and suicidal behavior. The overarching hypothesis is that TBI enhances impulsivity, a risk factor for suicide particularly in response to stress, through inflammation and dysfunction of the serotonin system and frontal lobe circuitry. Recent research increasingly highlights mild traumatic brain injury (mTBI) as a risk factor for suicidal thoughts and behaviors, including death by suicide. A study by Co-I Brenner found that Veterans with mTBI died by suicide at 1.8 the rate of the general Veteran population. The elevated suicide risk in Veterans with TBI is also consistent with previous research in civilians. Nevertheless, the study of suicide among those with mTBI is limited and there exists minimal understanding of the mechanism underlying this enhanced suicide risk in mTBI. There is a growing appreciation of the role of dysfunction in the circuits and white matter tracts underlying decision making in individuals with mTBI and history of a suicide attempt. However, neuroimaging studies examining the intersection of suicidal behavior and mTBI are limited. Moreover, how impulsivity and mTBI influences the development of suicidal behavior is also unclear. This project aims to address this gap with a neuroimaging project examining facets of impulsivity in Veterans with mTBI and a suicide attempt history. The James J. Peters VA (JJPVA) site proposes to investigate in male and female OEF/OIF/OND Veterans (n=140), the relationship of cognitive and behavioral impulsivity using a 2 (mTBI+/-) x 2 (history of suicide attempt (SA)+/-) design approach. Specifically, we will be examining four groups of Veterans: mTBI+/ SA+, mTBI+/SA-, mTBI-/SA+ and mTBI-/SA-. This project complements the animal studies being conducted at the New Jersey VA site by utilizing the same paradigms in humans during fMRI: the Go/No-go (motor) and Delay discounting (cognitive) task to assess impulsivity in both animals and humans. A primary objective of this study is to characterize alterations in brain activity and functional connectivity related to motor and cognitive impulsivity during fMRI in our four groups of Veterans. The secondary objective is to examine the relationship between white matter integrity using diffusion tensor imaging (DTI), and dynamic causal modeling with data from our two behavioral tasks of impulsivity performed during fMRI, along with psychometrically-validated measures of impulsivity. The third objective will be to determine similarities and differences in impulsivity data from animal TBI models and humans. All Veterans will receive rigorous diagnostic assessments, measures of impulsivity, clinical assessments of suicidal behavior, and a MRI scan (including structural MRI, DTI, and fMRI while performing impulsivity tasks). Blood will also be obtained for biomarker analysis, conducted by the Indianapolis VA site. Identifying potential neurobiological biomarkers for heightened suicide risk in Veterans with mTBI is essential for developing targeted care. The proposed research is translational as similar parallel analyses will be performed in humans and animals for investigating common neuronal circuits activated by impulsivity and genomic biomarkers.